The objective of this research project is to elucidate the role of fibrogenic factors in silicosis. Rabbit alveolar marcrophages are inflammatory secretory cells which generate many biologically active substances when cultured in vitro. The soluble factors elicited from these cells in vitro by a variety of inorganic dusts and particles will be tested for fibroblast growth promoting and fibrogenic activitiesutilizing the well-characterized human lung fibroblast line, HFL-1. The number of cultured cells, as well as the replication time, will be evaluated. Collagen production by the cultured fibroblasts will be measured utilizing both determinations of synthesized hydaaoxyproline residues and assessment of labeled proline and hydroxyproline residues in collagenase-sensitaive protein, thereby eliminating errors inhenrent in using either technique alone. The specific activity of the incorporated proline and hydroxyproline residues is proportional to that in the free intra-cellular proline pool of the cell mat. Using this value, the average number of poline residues incorporated into collagen per cell can be determined. The use of standard physicochemical techniques will achieve partial characterization of the active fibrogenic factor moieties. Any diversity of action found by bioassay on the cells will be related to either a qualitative or quantitative difference in the factors produced by macrophages subjected to the four above treatments. Broncho-pulmonary lavage fluids obtained from untreated control, latex injected rabbits and silica injected rabbits with fibrotic lung disease (at different time intervals post exposure) will be screened for fibrogenic factor. The series of physicochemical assays devised to characterize the in vitro factors will be used to establish relationships between the in vivo and in vitro produced factors. It has been postulated that the production of fibrogenic factors by alveolar macrophages is the central event in the pathogenesis of inorganic dust disease. The proposed experiments should establish the specificitry of in vitro production of fibrogenic factors by alveolar macrophages in response to fibrogenic particles and illuminate the role of such factors in the pathogenesis of silicosis.